1. Field of the Invention
This invention relates to a system for assembling wheels onto a car body conveyed in a state suspended by a hanger continuously (i.e., without being stopped).
2. Description of the Prior Art
Japanese Laid-Open Patent Publication No. 2-169303 discloses a system of assembling wheels onto a car body conveyed in a state suspended by a hanger. FIG. 21 schematically shows this system. As shown, the system mainly comprises a steering angle adjusting robot 212 and a wheel mounting robot 213 for adjusting the phase of a hub, setting a wheel on the phase-adjusted hub and then tightening hub nuts thereon.
The steering angle adjusting robot 212 can self-run between a front wheel mounting position 215 of a stationary car body 211 and a retracted position 214. The wheel mounting robot 213 can self-run toga front and a rear wheel mounting position 215 and 216 of the stationary car body 211 and to a wheel receiving position 217.
This wheel assembling system assembles wheels onto the car body 211 by executing a series of routine steps shown in FIG. 21.
(1) First, the hanger suspending the car body 211 is stopped to hold the car body 211 stationary.
(2) Then, the wheel mounting robot 213 receives a wheel for the reap wheel. At this time, the robot receives the wheel with the phase (hub bolt insertion hole angle) thereof preliminarily adjusted.
(3) Then, the robot 213 is moved to the rear wheel mounting position 216.
(4) Then, the robot 213 adjusts the phase (i.e., hub bolt position angle) of the rear wheel hub.
(5) Then, the robot 213 sets the wheel onto the rear wheel hub, that is, inserts each hub bolt into each hub bolt insertion hole. At this time, the wheel is set onto the hub by moving the wheel toward the hub since the phases of the wheel and hub have been adjusted in the steps (2) and (4) noted above.
(6) Then, the robot 213 tightens each hub nut on each hub bolt, thus bringing an end to the assembling of the rear wheel.
(7) Then, the robot 213 is returned to the wheel receiving position 217.
(8) Then, the robot 213 receives a wheel for the front wheel. Again at this time, the robot 213 receives the wheel with the phase thereof preliminarily adjusted.
(9) Then, the robot. 213 is moved to the front wheel mounting position 215.
During the steps (2) to (8), the steering angle adjusting robot 212 executes the following routine steps.
1! The robot 212 is moved from the retracted position 214 to the front wheel mounting position 215. PA1 2! Then, the robot 212 orients the front wheel hub in a predetermined direction, that is, adjusts the steering angle of the hub. PA1 3! Then, the robot 212 is returned to the retracted position 214. PA1 (a) The hanger which suspends and conveys the car body 211 is repeatedly started and stopped in a timed relation to the time required for the operation of assembling wheels on one car body (hereinafter referred to as cycle time). PA1 (b) The hanger which is repeatedly started and stopped is disadvantageous in view of the installation cost and maintenance compared to a hanger which conveys the car body continuously, i.e., without stop. PA1 (c) On the car body 211, an engine and a suspension are assembled as well as wheels. Therefore, usually the cycle time of the wheel assembling operation, that of the engine assembling operation and that of the suspension assembling operation are not equal. It is therefore impossible to convey the car body with a single conveyor over the engine, suspension and wheel assembling zones, that is, it is necessary to provide a conveyor for each of these zones. In addition, it is necessary to transfer the car body from the conveyor in one zone to the conveyor in another zone. PA1 (d) In the prior art system, the wheel mounting robot 213 undertakes the operations of hub phase adjusting, wheel setting and hub nut tightening. Therefore, the wheel mounting robot 213 has to perform a large number of operations in succession, thus leading to long cycle times. PA1 (A) correcting the steering angle and matching the phase of each front wheel hub; PA1 (B) matching the phase of each rear wheel hub; PA1 (C) setting a front wheel onto each front wheel hub and tightening each hub nut thereon; and PA1 (D) setting a rear wheel onto each rear wheel hub and tightening each hub nut thereon;
The step 3! is executed before execution of the step (9) to avoid mutual interference of the robots 212 and 213.
Subsequent to the step (9), the wheel mounting robot 213 executes the following steps.
(10) The robot 213 adjusts the phase of the front wheel hub.
(11) Then, the robot 213 sets the wheel onto the front wheel hub.
At this time, the wheel can be set onto the front wheel hub by moving the wheel toward the hub since the phases of the wheel and hub have been adjusted in the steps (8) and (10) and the steering angle or,the front hub has been adjusted in the step 2!.
(12) Then, the wheel mounting robot 213 tightens the hub nut on the hub bolt, thus bringing an end to the front wheel assembling.
(13) Then, the robot 213 is returned to the wheel receiving position 217 to be ready for the routine of mounting wheels onto the next car body.
(14) After the above routine has been over, the hanger movement is resumed to move the car body 211 to an extent corresponding to one car.
The above routine is repeated on the next car body to assemble wheels thereon.
The above wheel assembling system is very excellent, but it still has the following points for improvement.